This invention pertains to a method and apparatus for stacking sheets of paper or another material.
More particularly, this invention pertains to a method and apparatus which prevents the top sheet of a stack of paper from being dragged out of position when the first sheet of paper in a second stack slides over the top sheet.
Stacking apparatus for forming offset stacks of paper is well known. Each stack comprises a plurality of equal sized sheets stacked in registration one on top of the other. A conveyor belt delivers sheets for stacking. After the apparatus forms one stack of sheets against a paper stop, the paper stop is displaced and a second paper stop is moved into position. The second paper stop is offset from the first paper stop. A second stack of sheets forms against the second paper stop. The second stack is offset from the first stack. The back of each stack is defined as the portion of each stack that is near the conveyor belt which delivers the sheets which form and comprise the stack. The front of each stack is defined as the portion of each stack that is adjacent the paper stop or stops which halt the travel of each sheet in the stack after the sheet is xe2x80x9cthrownxe2x80x9d or slid by the conveyor onto the stack.
One problem which is encountered in conventional stacking apparatus is that the initial sheet in the second stack of sheets slides over the top sheet in the first stack of sheets. When the initial sheet slides over the top sheet of the first stack, the initial sheet tends to drag frictionally the top sheet out of registration with the remaining sheets in the first stack. A typical solution for this problem is to include in the stacking apparatus a system for grabbing and holding the back of the first stack while the initial sheet in the second stack slides over the top of the first stack. This solution is dependent on the back of the stack being in a certain position to within a relatively small tolerance. As a result, attempting to prevent the displacement of the top sheet of the first stack by holding the back of the first stack is not always reliable.
Accordingly, it would be highly desirable to provide an improved method and apparatus for preventing the top sheet in a stack of sheets from being frictionally displaced by a sheet that slides over the top sheet.
Therefore, it is a principal object of the instant invention to provide an improved method and apparatus for stacking sheets of paper or other material in offset relationship.
Another object of the invention is to provide an improved method and apparatus for stacking a second stack of registered sheets on a first stack of registered sheets so that the sheets in the second stack do not cause sheets in the first stack to move out of registration with other sheets in the first stack.
Briefly, in accordance with the invention, I provide an improved apparatus for stacking sheets in offset stacks. The apparatus includes a delivery system for delivering individual sheets; a support surface; a first paper stop; and a second paper stop. The first paper stop stops the movement of sheets delivered by the delivery system and is moveable between at least two operative positions, a first storage position and a second deployed position. In the second deployed position, the paper stop stops sheets delivered by the delivery system to form a first stack of sheets on the support surface. The first stack has a forward position adjacent the first paper stop. The second paper stop has a deployed position for stopping sheets delivered by the delivery system to form a second stack of sheets on the support surface above and offset from the first stack of sheets. The apparatus also includes a system for clamping the forward portion of the first stack when a sheet in the second stack frictionally slides over a sheet in the first stack.